Spectroscopic investigation of the symmetry breakdown in BIS-TTF compounds

The Vis-near IR absorption spectra of a bis-TTF molecule, 4,8-ethoxy-2,7-bis(benzo-1′,3′-dithiolyden)-1,3,5,7-teteratia-s-indacene (I) and of the monocationic species (I)+ generated by chemical or electrochemical oxidation are reported. The IR and Raman studies of (I) and the derived (I)xPF6 salt, as well as the ESR studies of (I)+ are described. The experimental results are compared with those of PM3 semi-empirical calculations. This comparison provides additional evidence for a symmetry breakdown in radical cations based on such bis-TTF systems. An asymmetric spin density distribution in the (I)+ radical cation is also confirmed by the ESR measurements.